Comments on: Timing the piston http://www.ret-monitor.com/articles/648/timing-the-piston/ Specific mission-critical info for professionals Fri, 18 May 2012 10:37:35 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: JC Biggs http://www.ret-monitor.com/articles/648/timing-the-piston/comment-page-1/#comment-3759 JC Biggs Wed, 21 Jul 2010 03:09:40 +0000 http://www.ret-monitor.com/articles/648/timing-the-piston/#comment-3759 Dan, i need to talk with you more about this cam setup. I build engines myself. but never as in depth as what i am doing now. im tryin to take a factor gsxr1000 motor and turn 19-20k rpm with it. I would love to have help specing a cam for it. Dan, i need to talk with you more about this cam setup. I build engines myself. but never as in depth as what i am doing now. im tryin to take a factor gsxr1000 motor and turn 19-20k rpm with it. I would love to have help specing a cam for it.

]]> By: Dan Zlock http://www.ret-monitor.com/articles/648/timing-the-piston/comment-page-1/#comment-1227 Dan Zlock Thu, 10 Dec 2009 01:13:54 +0000 http://www.ret-monitor.com/articles/648/timing-the-piston/#comment-1227 Excellent article, I agree completely.In excess of 40 years of motorcycle engine building I have witnessed the error of not enough piston to valve clearance. In recent years I have built many small displacement motorcycle roadracing engines, 600cc to 750cc. They commonly have large bores and short strokes with 4 large valves in the head. With any decent cam lift this arrangement makes it very difficult to increase the compression without parts hitting each other. In these engines any increase in compression will show a substantial gain in horsepower. The usual method of measuring piston to valve clearance is to sent the crankshaft at about 12 degrees btdc for the exhaust and about 12 degrees atdc for the intake. The engines are all DOHC inline 4 cylinder. Measurements could then be taken at 2 to 5 degree increments on each side of the starting point by compressing the valve to touch the piston. Usually the valve will very quickly reach the minimum clearance and just as quickly race away from the piston. Recent camshafts I have used that were not aftermarket but special factory only units displayed different characteristics. They have less lift than the stock street bike ones and about the same duration. If installed as is without any other engine modification they will make less power. They do have more piston to valve clearance though. This allows for a marked increase in compression by simply milling the head. Here is where the interesting feature shows up. When piston to valve is again set to minimum values the valve will track the piston at a minimum value of say .7mm for 20 to 25 degrees of crank rotation. The camshaft is ground so the valve motion mimics the piston motion when the parts are in close proximity. This allows compression gains that could not be done in any other way. I don't know how common this practice is in the car world but in the motorcycle world I have only seen cam design of this type in factory race parts. Regards, Dan Zlock Excellent article, I agree completely.In excess of 40 years of motorcycle engine building I have witnessed the error of not enough piston to valve clearance.

In recent years I have built many small displacement motorcycle roadracing engines, 600cc to 750cc. They commonly have large bores and short strokes with 4 large valves in the head. With any decent cam lift this arrangement makes it very difficult to increase the compression without parts hitting each other. In these engines any increase in compression will show a substantial gain in horsepower. The usual method of measuring piston to valve clearance is to sent the crankshaft at about 12 degrees btdc for the exhaust and about 12 degrees atdc for the intake. The engines are all DOHC inline 4 cylinder. Measurements could then be taken at 2 to 5 degree increments on each side of the starting point by compressing the valve to touch the piston. Usually the valve will very quickly reach the minimum clearance and just as quickly race away from the piston.

Recent camshafts I have used that were not aftermarket but special factory only units displayed different characteristics. They have less lift than the stock street bike ones and about the same duration. If installed as is without any other engine modification they will make less power. They do have more piston to valve clearance though. This allows for a marked increase in compression by simply milling the head. Here is where the interesting feature shows up. When piston to valve is again set to minimum values the valve will track the piston at a minimum value of say .7mm for 20 to 25 degrees of crank rotation. The camshaft is ground so the valve motion mimics the piston motion when the parts are in close proximity. This allows compression gains that could not be done in any other way.

I don’t know how common this practice is in the car world but in the motorcycle world I have only seen cam design of this type in factory race parts.

Regards,
Dan Zlock

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